Chemical preparation, crystallographic characterization, thermal behavior and IR studies of two new cyclotriphosphates SrKP3O9·3H2O and SrKP3O9

Strontium and potassium cyclotriphosphate trihydrate, SrKP3O9·3H2O, was prepared by ion-exchange resin. It crystallizes in the orthorhombic system Pnma, Z = 4 with the following unit-cell dimensions a = 9.082(2)Å, b = 8.133(2)Å, c = 15.009(2)Å and V = 1108.6(1)Å3. This salt is isotypic of SrRbP3O9·3H2O and SrNH4P3O9·3H2O whose crystal structure is determined by X-ray diffraction. Its thermal behavior is studied, between 25 and 800 °C, by infrared spectrometry, X-ray diffraction, thermal analyses TGA and DTA. SrKP3O9·3H2O leads, between 250 and 350 °C, to the corresponding anhydrous phase, SrKP3O9. This new phase is characterized crystallographically as isotype of SrRbP3O9. The calcination, between 400 and 650 °C, leads to a mixture of SrK2P4O12 crystallized and β[Sr(PO3)2] amorphous phase in X-ray diffraction. This mixture is stable until its melting point at 696 °C of SrK2P4O12. The kinetic characteristics of the dehydration of SrKP3O9·3H2O are determined. The vibrational spectrum of SrKP3O9·3H2O is examined and interpreted, in the domain of the valency frequencies, on the basis of the crystalline structure of its isotypic compounds SrMIP3O9·3H2O (MI = Rb+, Tl+) whose cycle has the site symmetry Cs. This infrared study is also made in the light of our results of the calculation of the IR frequencies and the successive isotopic substitutions of the equivalent atoms (3P, 3Oi and 6Oe belonging to the P3Oi3Oe6 ring) of the P3O93− cycle with symmetry Cs.